Atm multiplexing apparatus and cell discard method

ABSTRACT

An ATM multiplexing apparatus of the present invention is the apparatus for selectively performing cell discard processing in the case of congestion on the basis of a use state of the same connection formed by cells from the side of an ATM switching unit and subscribers without installing UPC units, and the ATM multiplexing apparatus, which is connected to the ATM switching unit and each of plural subscribers through ATM communication lines and performs multiplexing processing to ATM cells sent from the plural subscribers, comprises: detection means  118  for detecting a level of a congestion state corresponding to the received ATM  157  from the subscribers; and discard means ( 111, 115  and  117 ) for selectively discarding the received ATM cells from the subscribers on the basis of a communication state determined by the received ATM cells  155  from the ATM switching unit and the received ATM cells from the subscribers and a level value of a warning signal  129  indicating the detected congestion state.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention claims priority from Japanese Patent ApplicationNo. 10-374032 filed Dec. 28, 1998, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ATM (Asynchronous Transfer Mode)multiplexing apparatus, and particularly, to an ATM multiplexingapparatus for performing cell discard processing on the basis of acommunication state of the connection between ATM cells from the side ofan ATM switching unit and subscribers.

2. Description of Related Art

An ATM network communication system has become popular as service forintegrally conducting data communication including voice and text data,further image data requiring high-speed transmission. In the ATM networkcommunication system, cell discard processing is performed in order toprotect an ATM transmission band from an ATM cell caused by abnormalityetc. of subscriber terminals. The cell discard processing is carried outmainly by an ATM switching unit and an ATM multiplexing apparatus.

With regard to public known arts related to the present invention,technique on a control method of monitoring the packet flow rate isdisclosed in Japanese Unexamined Patent Publication No. 46344 of 1997.This control method provides a plurality of usage parameter controlmechanisms at the entrance of an ATM network. In each of the usageparameter control mechanism, the transfer rate defined in ABR (AvailableBit Rate) communication service is set as a monitor parameter. Thus,monitor operations according to the use state of the ATM network areexecuted. Also, technique on an ATM communication network comprising ATMswitching units connected in a multistage manner is disclosed inJapanese Unexamined Patent Publication No. 261244 of 1997. In this ATMcommunication network, if congestion has occurred in any of the ATMswitching units, an ATM switch of the fore-stage of the ATM switchingunit in which the congestion has occurred is notified of the congestion.The notified ATM switching unit controls the discard state of cells.Further, technique on a packet control switching unit and a celltransfer control method are disclosed in Japanese Unexamined PatentPublication No. 13427 of 1998. In this cell transfer control method, theATM switching unit acting as a node unit stores priority on cell discardcorresponding to a connection identifier. Cell discard processing iscontrolled on the basis of discard conditions determined by therelationship of the stored cell priority to the number of stack cells inthe node every connection.

FIG. 11 shows a conceptual diagram of a conventional ATM network system.An ATM switching unit 201 is installed in a central station. ATMmultiplexing apparatus 301 and 303 are largely installed at remote sitesnearest to subscribers. The ATM multiplexing apparatus 301 and 303desirably have a cheap and simple configuration where possible.

Functions necessary for the ATM multiplexing apparatus 301 and 303include a UPC (Usage Parameter Control) function. An object of the UPCfunction is to prevent congestion in an ATM network by checking whetherthe ATM cell flow from the subscribers violates a contract band or not.In order to efficiently share a band of an ATM transmission line withall the subscriber signals, the UPC to input signals of each subscriberline before multiplexing needs to be performed. However, installation ofthis UPC units 309 and 311 increases the cost per subscriber line. Onthe other hand, when SVC (Switched Virtual Connection) service forperforming dynamic signal setting is adopted, traffic settinginformation set by signaling needs to be passed between the ATMswitching unit and the ATM multiplexing apparatus. Passing of thetraffic setting information can be managed by installation of acommunication line for management, but the amount of processing of theATM multiplexing apparatus increases.

In the conventional ATM network system as shown in FIG. 11, the ATMmultiplexing apparatus 301 provides the UPC units 309 every subscriberline inside the units, so that the cost of installation increases. TheUPC unit 311 is installed inside of the ATM multiplexing apparatus 303to monitor a signal after multiplexing in a lump, so that the cost ofinstallation of the UPC unit 311 decreases. Even in the case ofinstalling any of the ATM multiplexing apparatus 301 and 303, trafficinformation from a traffic processing control part 211 is transferredfrom the ATM switching unit 201 to the ATM multiplexing apparatus 301and 303 through traffic information transfer means 213. The trafficinformation transfer means 213 means communication between respectiveunit control parts. Coping with the traffic information transfer means213 requires the increase in the cost of the ATM multiplexing apparatus301 and 303.

Under such circumstances, the ATM multiplexing apparatus and theselective cell discard method for performing cell discard processingefficiently in the case of congestion on the basis of a use state of theconnection formed by ATM cells received from the side of the ATMswitching unit and ATM cells received from the side of the subscriberswithout installing the UPC units have been desired. It is desirable todetect a congestion state corresponding to the ATM cell flow sent fromeach subscriber. It is desirable to sequentially update the use state ofthe connection on the basis of available information on the ATM cellsreceived from the ATM switching unit or the subscribers. The discardprocessing is desirably performed on the basis of a logical decisionusing a plurality of data providing the use state (communication state)of the connection and level information of the congestion state.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an ATM multiplexingapparatus and the cell discard method for selectively performing celldiscard processing on the basis of a level value of a congestion statecorresponding to each subscriber and a communication state of theconnection owned by each subscriber, and to provide an ATM multiplexingapparatus and the cell discard method for performing cell discardprocessing on the basis of a receiving interval of ATM cells from an ATMswitching unit or subscribers, and to provide criteria of discarddecision logic providing a basis of discard processing.

In order to achieve such an object, an ATM (Asynchronous Transfer Mode)multiplexing apparatus of the present invention is characterized by theATM multiplexing apparatus for being connected to an ATM switching unitand each of plural subscribers through ATM communication lines andperforming multiplexing processing to ATM cells sent from the pluralsubscribers, the ATM multiplexing apparatus comprising: detection meansfor detecting a congestion state corresponding to received ATM cellsfrom the subscribers and outputting a warning signal of a level valueaccording to the congestion state; and discard means for selectivelydiscarding the received ATM cells from the subscribers on the basis of ause state (communication state) of the same connection determined byreceived ATM cells 155 from the ATM switching unit and the received ATMcells from the subscribers and the level value of the congestion stateindicated by the warning signal from the detection means.

The above communication state is determined by header information andits received notification included in the received ATM cells from theATM switching unit or header information and its received notificationincluded in the received ATM cells from the subscribers.

The detection means desirably comprises storage means for storing thereceived ATM cells from the subscribers, and comparison means forgenerating the warning signal on the basis of the degree of occupancy inthe storage means of the stored ATM cells and the preset threshold.

Further, it is desirable that a plurality of detection means be providedand priority related to storage of the received ATM cells from thesubscribers be preset to each of the detection means. Also, each of thedetection means desirably comprises storage means for storing thereceived ATM cells from the subscribers and presetting the thresholdcorresponding to the priority, and comparison means for generating thewarning signal corresponding to the priority on the basis of the degreeof occupancy in the storage means of the stored ATM cells and the presetthreshold.

Moreover, the discard means desirably comprises switching unit monitormeans for receiving (monitoring) the ATM cells from the ATM switchingunit and outputting header information and received notification of thereceived ATM cells from the ATM switching unit as first headerinformation and first received notification, subscribermonitor/selection means for receiving (monitoring) the ATM cells fromthe subscribers and outputting header information and receivednotification of the received ATM cells from the subscribers as secondheader information and second received notification and selectivelydiscarding the received ATM cells from the subscribers on the basis of adiscard command, and discard control means for updating status dataindicating the communication state on the basis of the first headerinformation and the first received notification or the second headerinformation and the second received notification and generating thediscard command for commanding discard of the received ATM cells fromthe subscribers on the basis of the updated status data and the levelvalue of the warning signal.

The discard control means desirably comprises a status table for storingthe status data, which is formed of status flags and received time ofthe ATM cells from the ATM switching unit or the subscribers, on thebasis of an address corresponding to the first header information or thesecond header information, a table control part for responding to thefirst header information and the first received notification or thesecond header information and the second received notification andgenerating a control signal for commanding update of the status data, anelapsed time decision part for outputting a time-out signal on the basisof a comparison between the elapsed time from the received time to thepresent time of the status data read out responding to the controlsignal and the preset reference elapsed time, and a discard decisionpart for updating the readout status data on the basis of a signalrelated to either the first or second received notification and thetime-out signal and the second header information and generating thediscard command on the basis of the updated status data and the levelvalue of the warning signal.

The discard command is generated by the updated status data and thelevel values of a plurality of the warning signals, and may includeinformation specifying any of a plurality of the provided detectionmeans as the target storage of the received ATM cells from thesubscribers. The updated status data (updated status flags) is generatedon the basis of criteria of the preset state transition. The discardcommand is generated on the basis of criteria of the preset discarddecision logic. The status flags are formed by connection data “ACTIVE”or “SUSPEND” providing a two-way connection state established by thereceived ATM cells from the ATM switching unit and the received ATMcells from the subscribers, position data “BOM” or “COM” providing aposition of the received ATM cells from the subscribers in a packetsignal corresponding to an ATM adaptation layer (AAL5), discard data“DISCARDING” providing whether cell discard processing corresponding tothe packet signal is performed or not when the ATM cells from thesubscribers constitute the packet signal, and an AAL data “AAL5”indicating whether the received ATM cells from the ATM switching unitand the subscribers constitute the packet signal or not.

A discard method of ATM cells according to the ATM multiplexingapparatus of the present invention comprises the steps of receiving ATMcells sent from subscribers and detecting a congestion state of thereceived ATM cells from the subscribers, updating data providing acommunication state of the connection determined by the received ATMcells from the subscribers and received ATM cells from an ATM switchingunit responding to receipt of the ATM cells from the subscribers or theATM switching unit, deciding whether discard processing of the receivedATM cells from the subscribers is performed or not on the basis of theupdated data and a level value of a signal indicating the congestionstate, and selectively performing the discard processing on the basis ofthe decision result.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of an asynchronous transfer mode (hereinafter called ATM)multiplexing apparatus and an ATM cell discard method of the presentinvention will be described in detail with reference to the accompanyingdrawings below.

FIG. 1 is a block diagram illustrating an ATM network communicationsystem according to the first embodiment of the present invention;

FIG. 2 is a block diagram illustrating an ATM multiplexing apparatusaccording to the first embodiment of the present invention;

FIG. 3 is a block diagram illustrating a discard control part in the ATMmultiplexing apparatus according to the first embodiment of the presentinvention

FIG. 4 is an illustration of the format of a status table in the ATMmultiplexing apparatus according to the first and second embodiments ofthe present invention;

FIGS. 5A and 5B are conceptual diagrams illustrating a part ofprocessing of the discard control part in the ATM multiplexing apparatusaccording to the first and second embodiments of the present invention;

FIGS. 6A and 6B are conceptual diagrams illustrating a part ofprocessing of the discard control part in the ATM multiplexing apparatusaccording to the first embodiment of the present invention;

FIG. 7 is a flowchart illustrating operations of cell discard processingof the ATM multiplexing apparatus according to the first embodiment ofthe present invention;

FIG. 8 is a block diagram illustrating an ATM multiplexing apparatusaccording to the second embodiment of the present invention;

FIG. 9 is a block diagram illustrating a discard control part in the ATMmultiplexing apparatus according to the second embodiment of the presentinvention

FIG. 10 is a conceptual diagram illustrating a part of processing of thediscard control part in the ATM multiplexing apparatus according to thesecond embodiment of the present invention; and

FIG. 11 is a block diagram illustrating a conventional ATM networkcommunication system and ATM multiplexing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 which shows a block diagram of an ATM networkcommunication system receiving ATM multiplexing apparatus of the presentinvention, this ATM network communication system comprises an ATMswitching unit 101 and ATM multiplexing apparatus 109. The ATM switchingunit 101 is arranged in a station. The ATM switching unit 101 isconnected to ATM transmission lines (ATM communication lines) A.

The ATM switching unit 101 comprises a switch part 103, UPC (UsageParameter Control) units 105, and a traffic processing control part 107.The switch part 103 switches the direction of signals (ATM cells) fromsubscribers. The switched signals are connected to an ATM networkthrough the ATM transmission lines A. The UPC units 105 monitor whethermultiplexing signals 112 from the ATM multiplexing apparatus 109 violatethe contracted traffic or not. The traffic processing control part 107responds to the signaling connection request (not shown) from thesubscribers and performs connection processing of the requestedconnection.

The ATM multiplexing apparatus 109 are arranged in the side of thesubscribers corresponding to the number of UPC units 105 provided in theATM switching unit 101, and are connected to the ATM switching unit 101through ATM transmission lines B and are connected to the signals (ATMcells) from the subscribers through ATM transmission lines C.

The ATM multiplexing apparatus 109 comprises a cell header monitor part(switching unit monitor means) 111, a multiplexing part 113, discardcontrol parts (discard control means) 115, and cell filters (subscribermonitor/selection means) 117.

The cell header monitor part 111 monitors ATM cells transmitted from theside of the ATM switching unit to the side of the subscribers andacquires header information. The monitored ATM cells from the ATMswitching unit are transmitted to the ATM transmission lines C as ATMcells (hereinafter called received ATM cells) 155 received from the ATMswitching unit. Also, the cell header monitor part 111 outputs headerinformation (first header information) and its received notification(first received notification) 125 acquired from the received ATM cells155 from the ATM switching unit. The first header information includes aVPI (Virtual Pass Identifier) and a VCI (Virtual Channel Identifier).

The multiplexing part 113 performs multiplexing processing to ATM cellsfrom the respective cell filters 117 and generates a multiplexing signal112. The multiplexing part 113 detects a congestion state if the amountof retention of the received ATM cells from the subscribers exceeds thepreset threshold. The detected congestion state is generated as awarning signal 129. The discard control part 115 pairs off with the cellfilter 117 and they are provided corresponding to the number ofsubscribers.

The discard control part 115 updates status data 139 (as described inFIGS. 3 and 4 below) indicating a communication state on the basis ofthe first header information and the first received notification 125from the cell header monitor part 111 or the second header informationand the second received notification 127. Further, the discard controlpart 115 responds to the warning signal 129 from the multiplexing part113, and decides whether the received ATM cells from the subscribers arediscarded or not on the basis of a level value of the warning signal 129and the updated status data, and generates a discard command 131 as thedecision result.

The cell filter 117 monitors ATM cells 126 from the subscribers andacquires header information. The monitored ATM cells from thesubscribers are temporarily stored in the cell filter 117 as ATM cells(hereinafter called received ATM cells) received from the subscribers(not shown). Also, the cell filter 117 outputs header information(second header information) and its received notification (secondreceived notification) 127 acquired from the received ATM cells from thesubscribers. The second header information includes a PTI (Payload TypeIdentifier) in addition to the VPI and the VCI. Moreover, the cellfilter 117 discards the received ATM cells from the subscribers storedtemporarily on the basis of the discard command 131 from the discardcontrol part 115, or transfers (passes) the received ATM cells to themultiplexing part 113. FIG. 2 shows the received ATM cells 157′ from thesubscribers in the case of being transferred.

Thus, the ATM multiplexing apparatus 109 of the present inventionselectively discards the received ATM cells from the subscribers. Thisselective discard processing is performed on the basis of the levelvalue of the warning signal 129 from the multiplexing part 113 and thecommunication state. The communication state in this case indicates ause state of the same connection determined by the received ATM cells155 from the ATM switching unit and the received ATM cells from thesubscribers.

FIG. 2 shows a detailed block diagram of the ATM multiplexing apparatus109 in the ATM network communication system of the present invention.The multiplexing part 113 comprises detection means 118 and a readoutcontrol part 123.

In the present embodiment, one detection means 118 is providedcorresponding to a subscriber line (or a pair of the discard controlpart 115 and the cell filter 117). The detection means 118 comprisesstorage means 119 and comparison means 121.

The storage means 119 stores the received ATM cells from thesubscribers. The comparison means 121 holds the preset threshold. Thecomparison means 121 generates the warning signal 129 on the basis ofthe degree of occupancy in the storage means 119 of the ATM cells storedin the storage means 119 and the preset threshold. The warning signal129 provides the level value corresponding to the preset threshold.Also, the storage means 119 generates the warning signal 129 indicatinga congestion state if the above degree of occupancy exceeds the presetthreshold. As described below, if the threshold, for example, is set to“½”, the warning signal 129 is generated as “0” or “1”. Also, if aplurality of the thresholds, for example, are set to “⅝”, “¾”, and “⅞”,the warning signal 129 provides the level values of “000”, “001”, “011”or “111”. The readout control part 123 sequentially reads out the ATMcells stored in the respective storage means 119, and transmits the ATMcells to the ATM transmission lines B as the multiplexing signal 112. Inthe present invention, a readout control method is not limited.

FIG. 3 shows a detailed block diagram of the discard control part 115 asindicated in FIG. 2. Referring to FIG. 3, the discard control part 115comprises a table control part 132, a status table 137, a first register141, a second register 143, a discard decision part 147, an elapsed timedecision part 151, and a timer counter 153.

The table control part 132 responds to the first header information(VPI, VCI) 125 a and the first received notification 125 b or the secondheader information (VPI, VCI) 127 a and the second received notification127 b, and generates a control signal 133. The control signal 133 is asignal for commanding updating of status data 139, and includes adirective signal 133 a of the address corresponding to the first headerinformation 125 a or the second header information 127 a and a sendingend signal 133 b. The sending end signal 133 b provides a sending sourceindicating that the received ATM cells have been received from the sideof either the ATM switching unit or the subscribers. Thus, the sendingend signal 133 b is a signal associated with either the first receivednotification 125 b or the second received notification 127 b.

The status table 137 stores the status data 139 on the basis of theaddress corresponding to the first header information 125 a or thesecond header information 127 a. The format (the status data 139) of thestatus table 137 is shown in FIG. 4. The status data 139 provides theabove-mentioned communication state. The status data 139 is formed ofstatus flags 139 a and received time (time stamp) 139 b of the ATM cellsfrom the ATM switching unit or the subscribers. Details of the statusflags 139 a are described below. Also, the status table 137 outputs thestatus data 139 corresponding to the address indicated by the directivesignal 133 a of the address as status data 135 using time divisionprocessing.

The first register 141 temporarily stores the status data 135 read outfrom the status table 137 and the sending end signal 133 b. The secondregister 143 temporarily stores the status data updated by the discarddecision part 147 and that time. The elapsed time decision part 151calculates the elapsed time from the received time 139 b to the presenttime 154. The received time 139 b is included in the status data 135read out responding to the control signal 133 (directive signal 133 a ofthe address). The present time 154 is generated by the timer counter153. A time interval of the timer counter 153 is the order of severalhundreds of milliseconds to a second and may be set in apparatus unit.Further, the elapsed time decision part 151 compares the calculatedelapsed time with a preset reference elapsed time 149. The elapsed timedecision part 151 generates a time-out signal 152 if it is decided thatthe calculated elapsed time has exceeded the preset reference elapsedtime 149. The preset reference elapsed time 149 is held in the elapsedtime decision part 151 and is variably set from the outside.

The discard decision part 147 updates the readout status data 135 on thebasis of the sending end signal 133 b, the time-out signal 152 and thesecond header information (PTI) 127 c using the sending end signal 133 b(signal related to any of the first or second received notification)from the first register 141 and the readout status data 135, thetime-out signal 152 from the elapsed time decision part 151 and furtherthe second header information (PTI) 127 c as input. In this updateprocessing, each component of the status flags 139 a in the status data135 read out is updated on the basis of criteria of the state transitionshown in FIG. 5. Moreover, the received time 139 b in the status data135 read out is updated by the present time from the timer counter 153.Each of the updated data is again stored in the status table 137 as theupdated status data 145 through the second register 143. The criteria ofthe state transition will be described below. Further, the discarddecision part 147 generates the discard command 131 on the basis ofcriteria of discard decision logic shown in FIG. 6 when the warningsignal 129 indicating the congestion state is inputted in the case ofthe above update processing. The criteria of discard decision logic willbe described below.

Incidentally, for convenience of description, the first and secondregisters (141 and 143), the discard decision part 147 and the elapsedtime decision part 151 are individually shown in the present embodiment,but they are preferably integrated on one LSI (Large Scale Integration).

FIG. 4 shows the format of the status table 137 (status data 139). Thestatus data 139 is formed of status flags 139 a and received time (timestamp) 139 b. Also, in this example, the status flags 139 a are formedof connection data (ACTIVE/SUSPEND) 139 a 1, position data (BOM/COM) 139a 2, discard data (DISCARDING) 139 a 3, and AAL data (AAL5) 139 a 4. Theconnection data (ACTIVE/SUSPEND) 139 a 1 indicates a two-way connectionstate of the same connection established by the received ATM cells 155from the ATM switching unit and the received ATM cells from thesubscribers. The position data (BOM/COM) 139 a 2 indicates the where thereceived ATM cells from the subscribers. are positioned in a packetsignal corresponding to an ATM adaptation layer (AAL)5. “BOM” meansBeginning Of Message of the packet signal, and “COM” means ContinuationOf Message of the packet signal. The discard data (DISCARDING) 139 a 3indicates whether cell discard processing constituting the packet signalcorresponding to the ATM adaptation layer (AAL)5 is performed or not.The AAL data (AAL5) 139 a 4 indicates whether the received ATM cells 155from the ATM switching unit and the received ATM cells from thesubscribers constitute the packet signal corresponding to the above AAL5or not.

FIGS. 5A and 5B show diagrams of criteria of the state transition. Theupdate processing in the discard decision part 147 as described above isperformed on the basis of the criteria of the state transition. FIG. 5Aprovides the state transition of the connection data (ACTIVE/SUSPEND)139 a 1. FIG. 5B provides the state transition of the AAL data (AAL5)139 a 4.

Referring first to FIG. 5A, the discard decision part 147 sets a state(connection data 139 a 1) of the connection specified by cellinformation (VPI, VCI) of the received ATM cells from the subscribers toa “SUSPEND” state when a receiving end signal 133 b related to thesecond received notification 127 b is inputted (transition 0, includinginitial state). In the state of transition 0, the discard decision part147 holds the state of the connection data 139 a 1 read out through thefirst register 141 with the “SUSPEND” state when the receiving endsignal 133 b related to the second received notification 127 b isinputted (transition 1). In the state of transition 0, the discarddecision part 147 updates the connection data 139 a 1 to an “ACTIVE”state when a receiving end signal 133 b related to the first receivednotification 125 b is inputted (transition 2). In the state oftransition 2, the discard decision part 147 holds the connection data139 a 1 with the “ACTIVE” state when the receiving end signal 133 brelated to the first received notification 125 b is inputted (transition3). In the state of transition 2, the discard decision part 147 performsprocessing based on a time-out signal 152 as shown below when thereceiving end signal 133 b related to the second received notification127 b is inputted. The discard decision part 147 holds the connectiondata 139 a 1 with the “ACTIVE” state when inputting only the receivingend signal 133 b related to the second received notification 127 b inthe “ACTIVE” state (transition 4). Also, the discard decision part 147updates the connection data 139 a 1 to the “SUSPEND” state wheninputting the time-out signal 152 as well as the receiving end signal133 b related to the second received notification 127 b in the “ACTIVE”state (transition 5).

Next, FIG. 5B will be described. When the packet signal corresponding tothe AAL5 is divided into ATM cells, the least significant bit of a PTIfield (3 bits) included in a cell header of the last cell is set to “1”.Thus, the discard decision part 147 responds to cell information (PTI)127 c and updates AAL data 139 a 4 when the received ATM cells from thesubscribers constitute the packet signal conforming to the AAL5. Thatis, the discard decision part 147 responds to the cell information (PTI)127 c providing “PTI=xx0” (where x is an arbitrary bit value) and setsthe AAL data 139 a 4 to a “COM” state (transition 00, including initialstate). In the state of transition 00, the discard decision part 147responds to the cell information (PTI) 127 c providing “PTI-xx1” andupdates the AAL data 139 a 4 to a “BOM” state (transition 01). In thestate of transition 01, the discard decision part 147 responds to thecell information (PTI) 127 c providing “PTI-xx0” and updates the AALdata 139 a 4 to a “COM” state (transition 02). In the state oftransition 02, the discard decision part 147 holds the AAL data 139 a 4to a “COM” state when inputting the cell information (PTI) 127 cproviding “PTI=xx0” (transition 02)

The following two states may be detected by the state transition diagramof FIG. 5A.

The first state is the state in which cell input only from thesubscribers is present and response cells from the ATM switching unit(ATM network side) are absent. This first state is the state in whichabnormal conditions have occurred in subscriber terminals or flowcontrol such as TCP/IP has not been performed in a high layer, and is apossibility of the unreliable connection in communication lines of onlyone way. In this case, input cells may be the abnormal cells or theunreliable connection. Thus, there is no serious problem even if theinput cells are discarded in congestion. The second state is the statein which arrival intervals of the cells from the subscribers haveelapsed longer than the preset time. That is, it is possible that theSVC connection is disconnected once and is switched to other connection.

The second state cannot continue the previous condition (“ACTIVE”state). Thus, the connection data 139 a 1 is updated to the “SUSPEND”state in order to again decide the state. Also, when the connection isnot disconnected, it may be decided that there is the connection havinglow traffic density. For low traffic density, there is a little load onthe ATM network even if the high layer executes resending after celldiscard. Therefore, there is no serious problem even if discardprocessing is performed in congestion.

In the case where the received ATM cells from the subscribers constitutethe packet signal corresponding to the AAL5, if one cell is discarded,all the packet signal is discarded in the high layer. When cell discardis carried out in a congestion state, packet discard technique fordiscarding the packet signal corresponding to the AAL5 except for thelast cell is used. Hence, in the present embodiment, the communicationstate is managed using the technique in conjunction with the criteria ofthe state transition as shown in FIG. 5B. When the cell discard in thepacket signal is carried out, the cells corresponding to the same packetsignal and the same connection are discarded except for the last cell.

As described above, the ATM multiplexing apparatus 109 of the presentinvention manages the communication state on the basis of the criteriaof the state transition as shown in FIGS. 5A and 5B. This sequentiallyupdated communication state (status data 139) provides decisionmaterials in the case of discard decision processing as described below.

FIGS. 6A and 6B show criteria of discard decision logic. Here, thecriteria of discard decision in the case that the level value ofcongestion given by a warning signal 129 is one kind and three kinds(“⅝”, “¾” and “⅞”) is indicated. On the basis of this criteria, thediscard decision part 147 performs the discard decision processing usingthe level value indicated by the warning signal 129 and the updatedstatus flags as decision materials when the warning signal 129indicating the congestion state is inputted.

Referring to FIG. 6A, decision 1 provides the decision in the case thatdiscard data 139 a 3 after the state transition is “DISCARDING” and thereceived ATM cells from the subscribers is not the last cell(“PTI=xx0”). In this case, the discard decision part 147 generates thediscard command 131 (for example, discard level “1”) intended for thecells except the last cell in spite of the level value of the warningsignal 129. When discard processing intended for the BOM cell or COMcell of the packet signal corresponding to the AAL5 is carried out, thediscard data 139 a 3 is updated to a “DISCARDING” state. Also, whenreceiving the last cell (inputting the cell information (PTI) 127 cproviding “PTI=xx1”), the “DISCARDING” state is released. Decision 2provides the decision in the case that the discard decision command 129is “1” (congestion state) and the connection data 139 a 1 is a “SUSPEND”state. In this case, the discard decision part 147 generates the discardcommand 131 in spite of the position data 139 a 2.

Referring to FIG. 6B, decision 1′ provides the decision in the case thatdiscard data 139 a 3 is the “DISCARDING” state and the received ATMcells from the subscribers is not the last cell (“PTI=xx0”). In thiscase, the discard decision part 147 generates the discard command 131 inspite of the level value of the warning signal 129. Decision 2 providesthe decision in the case of inputting the warning signal 129 giving thelevel value “001”. In this case, the discard decision part 147 generatesthe discard command 131 when the connection data 139 a 1 is the“SUSPEND” state and the position data 139 a 3 is “BOM”. At this time,the discard data 139 a 3 is updated to the “DISCARDING” state. Decision3′ provides the decision in the case of inputting the warning signal 129giving the level value “011”. In this case, the discard decision part147 generates the discard command 131 when the connection data 139 a 1is the “SUSPEND” state and the position data 139 a 3 is “COM”. Decision4′ provides the decision in the case of inputting the warning signal 129giving the level value “111”. In this case, the discard decision part147 generates the discard command 131 when the position data 139 a 2 isthe “BOM” state even if the connection data 139 a 1 is the “ACTIVE”state. At this time, the discard data 139 a 3 is updated to the“DISCARDING” state.

The ATM multiplexing apparatus of the present invention takescommunication of the packet signal corresponding to the AAL5 intoconsideration. The AAL5 is in the most use in data communication on anATM network. As to a procedure, the initial value of the position data139 a 2 of the received ATM cells constituting the packet signalcorresponding to the AAL5 is set to the “COM” state. Next, responding tothe second header information (“PTI=xx1”) 127 c, the position data 139 a2 is updated to the “BOM” state. At this time, the AAL5 data 139 a 4 isset to “ON”. Further, the discard data 139 a 3 is updated to the“DISCARDING” state only if the AAL5 data 139 a 4 is the “ON” state.Thus, the legality of packet discard processing is assured. Also, in theabove discard processing, when the CBR traffic by an AAL1 flows, theposition data 139 a 2 is held to the“COM” state. In this case, the celldiscard processing is not performed since the AAL5 data is not updatedto the “ON” state.

On the other hand, when detection means 109 in the ATM multiplexingapparatus 109 does not detect the congestion state, namely, outputcapacity in the case of applying multiplexing processing to an ATMsignal from the subscribers is not more than output lines connected tothe ATM switching unit, the UPC units 105 arranged in the input part ofthe ATM switching unit 101 monitor the traffic of contract violation inthe output capacity after the multiplexing processing, and the input ofabnormal cells due to abnormality of the subscriber terminals.

FIG. 7 shows a flowchart illustrating a cell discard method of the ATMmultiplexing apparatus according to the first embodiment of the presentinvention.

Referring to FIGS. 2 and 7, first, in step S101, update processing ofstatus data 139 is executed. This update processing includes thereceived time 139. Also, the update processing responds to receipt ofATM cells 126 from the subscribers or ATM cells 124 from the ATMswitching unit, and is sequentially performed on the basis of thecriteria of the state transition shown in FIG. 5 as described above.Next, in step S102, detection processing of a congestion state of thereceived ATM cells from the subscribers is carried out. In thisdetection processing, the case that the congestion state is not detectedis, for example, the case that the warning signal 129 providing thelevel value “0” in FIG. 6A as described above is inputted to the discarddecision part 147. In this case, processing of step S101 is performed.Then, when the congestion state is detected in step S102, operation isshifted to update processing (step S105) of the status data 139 (statusflags 139 a) through receipt (monitor) processing (step S104) of the ATMcells 126 from the subscribers. Further, in step S104, the same updateprocessing as step S101 is performed when receiving (monitoring) the ATMcells 124 from the ATM switching unit. After the update processing ofstep S105, in step S106, the discard decision part 147 decides whether apair of data of the level value of the warning signal 129 and theupdated status flags 139 a correspond to any of the criteria of discarddecision shown in FIGS. 6A and 6B as described above. In step S106, thediscard decision part 147 generates the discard command 131 (forexample, level value “1”) when it is decided that a pair of data of thelevel value of the warning signal 129 and the updated status flags 139 acorrespond to any of the criteria of the preset discard decision logic.After generation of the discard command 131 (for example, level value“1”), the discard decision part 147 updates or holds the discard data139 a 3 of the status flags 139 a to “DISCARDING”. Moreover, the discarddecision part 147 updates the received time 139 b to the present time154 and stores them in the status table 137 as the status data 145.Then, in step S107, the cell filter 117 responds to the discard command131 (for example, “1” or “0”) and selectively discards the received ATMcells from the subscribers stored temporarily.

The ATM multiplexing apparatus 109 in the first embodiment of thepresent invention selectively discards the ATM cells flowing into theATM network due to trouble etc. of the subscriber terminals in the caseof congestion of the subscriber side. Since each header of the receivedATM cells 155 from the ATM switching unit 101 (ATM network) is set bythe traffic processing control part 107 of the ATM switching unit 101,header information of the received ATM cells 155 from the ATM switchingunit is correct connection information. Among the received ATM cellsfrom the subscribers, the received ATM cells having the headerinformation different from the received ATM cells 155 from the ATMswitching unit may highly be abnormal cells caused one-sidedly from thesubscriber terminals, so that such cells are priority discarded. By thecriteria of the preset discard decision logic, cell discard processingin the case of a short arrival interval of cells decreases in comparisonwith the case of a long receipt interval of cells, so that packetdiscard in the case of transmitting a large amount of data throughTCP/IP etc. can be reduced. Also, in the cell discard processing in thepresent invention, connection setting information is unnecessary and itis unnecessary to dynamically receive to process actual connectioninformation held by the ATM switching unit 101, so that control circuitsin the ATM multiplexing apparatus can be configured at a low cost,thereby the ATM multiplexing apparatus itself can be configured at a lowcost.

Next, an ATM multiplexing apparatus and a cell discard method accordingto the second embodiment of the present invention will be described.FIG. 8 shows a block diagram of the ATM multiplexing apparatus accordingto the second embodiment of the present invention. Incidentally, bymarking like reference characters on components having the same functionas the above-mentioned first embodiment, description of the componentsis omitted.

Referring to FIG. 8, an ATM multiplexing apparatus 109 according to thepresent embodiment provides a plurality of detection means correspondingto subscriber lines. Priority related to storage of the received ATMcells from the subscribers is preset to each of a plurality of thedetection means. In the present embodiment, two classes of the detectionmeans (118-1, 118-2) are provided to one subscriber. Each of a pluralityof the detection means (118-1 or 118-2) provides storage means (119-1 or119-2) and comparison means (121-1 or 121-2). The storage means (119-1or 119-2) stores the received ATM cells from the subscribers. Thresholdcorresponding to the priority is preset in the storage means. Thecomparison means (121-1 or 121-2) generates a warning signal (129-1 or129-2) corresponding to the priority on the basis of the degree ofoccupancy in the storage means of the stored ATM cells and the presetthreshold. The warning signal (129-1 or 129-2) provides the level valuecorresponding to the preset threshold. In the case of providing thestorage means in which the priority is respectively set, a use state ofthe same connection managed by the status flags 139 a can be utilizedfor priority decision. A readout control part 132 executes cell readoutprocessing from the storage means 119-1 always taking higher prioritythan cell readout processing from the storage means 119-2.

FIG. 9 shows a block diagram of a discard control part 115′. FIG. 9corresponds to FIG. 3 in the above-mentioned first embodiment. Thedifference between FIG. 9 and FIG. 3 is that a discard decision part147′ inputs the warning signals (129-1, 129-2 shown in FIG. 9) generatedfrom a plurality of the detection means (storage means). The discarddecision part 147′ performs discard decision processing on the basis ofthe level value indicated by the warning signals and the updated statusdata 139 (status flags) when inputting the warning signals (129-1,129-2) indicating the congestion state. Update processing of the statusdata 139 is the same processing as the above-mentioned first embodiment.

The discard decision processing is performed on the basis of criteria ofdiscard decision logic shown in FIG. 10. The criteria shown in FIG. 10is construed as the decision criteria in the case of inputting thewarning signal 129 (level value) of FIG. 6B in the above-mentioned firstembodiment to the discard decision part 147 simultaneously.

Referring to FIG. 10, decision 1″ provides the decision in the case thatdiscard data 139 a 3 after the state transition is “DISCARDING” and thereceived ATM cells from the subscribers is not the last cell(“PTI=xx0”). In this case, the discard decision part 147′ generates thediscard command 131′ (discard level “1”) intended for the cells exceptthe last cell in spite of the level values of the warning signals 129-1and 129-2. Next, decision 2″ provides the decision in the case that eachof the level values of the warning signals 129-1 and 129-2 is “1”(congestion state) and the connection data 139 a 1 is a “SUSPEND” state.In this case, the discard decision part 147′ generates the discardcommand 131′ (discard level “1”) in spite of the position data 139 a 2.Further, decision 3″ provides the decision in the case that each of thelevel values of the warning signals 129-1 and 129-2 gives “0” and “1”.In this case, the discard decision part 147′ generates the discardcommand 131′ (pass level “0”) when the connection data 139 a 1 is the“SUSPEND” state in spite of the position data 139 a 3. This discardcommand 131′ includes indication of the target storage (storage means119-1). Moreover, decision 4″ provides the decision in the case thateach of the level values of the warning signals 129-1 and 129-2 gives“1” and “0”. In this case, the discard decision part 147′ generates thediscard command 131′ (pass level “0”) when the connection data 139 a 1is the “SUSPEND” state in spite of the position data 139 a 3. Thisdiscard command 131′ includes indication of the target storage (storagemeans 119-2). Further, decision 5″ provides the decision in the casethat each of the level values of the warning signals 129-1 and 129-2gives “0”. In this case, the discard decision part 147′ generates thediscard command 131′ (pass level “0”) when the connection data 139 a 1is the “ACTIVE” state in spite of the position data 139 a 3. Thisdiscard command 131′ includes indication of the target storage (storagemeans 119-1).

A cell filter 117′ responds to the discard command 131′ from the discarddecision part 147′ and selectively performs the cell discard processing.Also, the cell filter 117 transfers the received ATM cells 157 from thesubscribers to the storage means 119-1 or 119-2 indicated by the discardcommand 131′.

By the ATM multiplexing apparatus according to the present embodiment,the cell discard processing with the amount of discard reduced isimplemented. Also, by setting the level values of the congestion statedifferent each other, discard processing of the packet signalcorresponding to the AAL5 may also be used in the same manner as theabove-mentioned first embodiment.

Incidentally, the present invention is not limited to the criteria ofstate transition and the criteria of discard decision logic (content ofdecision items) defined in the above-mentioned first and secondembodiments, and the criteria are preset variably.

As described above, the ATM multiplexing apparatus according to thepresent invention implements selective discard processing to thereceived ATM cells from the subscribers in the case of congestion. Bymanaging a use state of the connection on the basis of informationeasily acquired from the received ATM cells from the subscribers and thereceived ATM cells from the ATM switching unit, the selective discardprocessing is performed.

1. An ATM (Asynchronous Transfer Mode) multiplexing apparatus for beingconnected to an ATM switching unit and each of plural subscribersthrough ATM communication lines and performing multiplexing processingto ATM cells sent from the plural subscribers, the ATM multiplexingapparatus comprising: detection means for detecting a congestion statecorresponding to received ATM cells from the subscribers and outputtinga warning signal of a level value according to the congestion state; anddiscard means for selectively discarding the received ATM cells from thesubscribers on the basis of a communication state determined by receivedATM cells from the ATM switching unit and the received ATM cells fromthe subscribers and the level value of the congestion state indicated bythe warning signal from the detection means.
 2. An ATM multiplexingapparatus as defined in claim 1, wherein the communication state isupdated on the basis of header information and its received notificationincluded in the received ATM cells from the ATM switching unit or headerinformation and its received notification included in the received ATMcells from the subscribers.
 3. An ATM multiplexing apparatus as definedin claim 1, wherein the detection means comprises storage means forstoring the received ATM cells from the subscribers, and comparisonmeans for generating the warning signal on the basis of the degree ofoccupancy in the storage means of the stored ATM cells and the presetthreshold.
 4. An ATM multiplexing apparatus as defined in claim 1,wherein the discard means comprises: switching unit monitor means forreceiving the ATM cells from the ATM switching unit and outputtingheader information and received notification of the received ATM cellsfrom the ATM switching unit as first header information and firstreceived notification; subscriber monitor/selection means for receivingthe ATM cells from the subscribers and outputting header information andreceived notification of the received ATM cells from the subscribers assecond header information and second received notification andselectively discarding the received ATM cells from the subscribers onthe basis of a discard command; and discard control means for updatingstatus data indicating the communication state on the basis of the firstheader information and the first received notification or the secondheader information and the second received notification and generatingthe discard command for commanding discard of the received ATM cellsfrom the subscribers on the basis of the updated status data and thelevel value of the warning signal.
 5. An ATM multiplexing apparatus asdefined in claim 4, wherein the status data is formed of status flagsand received time of the ATM cells from the ATM switching unit or thesubscribers, and the discard control means comprises: a status table forstoring the status data on the basis of an address corresponding to thefirst header information or the second header information; a tablecontrol part for responding to the first header information and thefirst received notification or the second header information and thesecond received notification and generating a control signal forcommanding update of the status data; an elapsed lime decision part foroutputting a time-out signal on the basis of a comparison between theelapsed time from the received time to the present time of the statusdata read out responding to the control signal and the preset referenceelapsed time; and a discard decision part for updating the readoutstatus data on the basis of a signal related to either the first orsecond received notification and the time-out signal and the secondheader information and generating the discard command on the basis ofthe updated status data and the level value of the warning signal.
 6. AnATM multiplexing apparatus as defined in claim 4, wherein the updatedstatus data is generated on the basis of criteria of the preset statetransition.
 7. An ATM multiplexing apparatus as defined in claim 4,wherein the discard command is generated on the basis of criteria of thepreset logic decision.
 8. An ATM multiplexing apparatus as defined inclaim 5, wherein the status flags include connection data providing atwo-way connection state established by the received ATM cells from theATM switching unit and the received ATM cells from the subscribers,position data providing a position of the received ATM cells from thesubscribers in a packet signal corresponding to an ATM adaptation layer(AAL)5, discard data providing whether cell discard processingcorresponding to the packet signal is performed or not when the ATMcells from the subscribers constitute the packet signal, and an AAL dataindicating whether the received ATM cells from the ATM switching unitand the subscribers constitute the packet signal or not.
 9. A discardmethod of ATM cells comprising the steps of: receiving ATM cells sentfrom subscribers and detecting a congestion state of the received ATMcells from the subscribers; updating data providing a communicationstate determined by the received ATM cells from the subscribers andreceived ATM cells from an ATM switching unit responding to receipt ofthe ATM cells from the subscribers or the ATM switching unit; decidingwhether discard processing of the received ATM cells from thesubscribers is performed or not on the basis of the updated data and alevel value of a signal indicating the congestion state; and selectivelyperforming the discard processing on the basis of the decision result.